Four main themes can be defined in the organization of clinical activities and in the development of clinical research programs in the Department of Radiotherapy: 1) the recognition of the criticality of tolerance to irradiation and the assessment of its effect on treatment results; 2) the initiation and establishment of modifications in basic radiation therapy techniques; 3) the combination of irradiation and surgery in the treatment of cancer; and 4) the use of radiation modifiers in the treatment of cancer. The Department of Radiotherapy is structured for an orderly study of malignant disease according to anatomical locations and the results achieved through specific treatment techniques and treatment modifications. It has been the practice to analyze continually the results of treatment and initiate modifications as needed to obtain maximum control rates with minimum complications. The two main functions of the Experimental Radiotherapy laboratory are to cooperate with the clinical staff in keeping abreast of new developments and to engage in more basic research. The research effort is the biochemistry of cell differentiation. The purpose of the Radiation Physics research program is a review and formalization of all treatment plans, treatment set-ups and calibrations used at the M. D. Anderson Hospital and combining these into set treatment systems now in use, by the automation of patient charts and machine monitoring, by a tumor registry using the PC-12 computer, and by the development of simulation techniques in radiotherapy.